1. Field of the Invention
The present invention relates to a semiconductor device having a base plateless structure that does not use a substrate fixing base plate.
2. Description of the Background Art
As disclosed in, for example, Japanese Patent Application Laid-open No. 7-326711 (FIGS. 1 and 5), there have conventionally been proposals of semiconductor devices having a base plateless structure that does not use a metallic or other base plate for fixedly placing a substrate on which semiconductor elements are to be formed. Other semiconductor devices as disclosed in Japanese Patent Application Laid-Open No. 9-69603 (FIG. 5) have also conventionally been proposed in which an external electrode is integrally molded with an outer case on the upper surface of the outer case by insert molding, and one end of the external electrode is attached to a circuit conductive foil on an insulating substrate located inside the case.
However, the following problems to be solved exist with the semiconductor devices according to the aforementioned conventional techniques.
The semiconductor device disclosed in Japanese Patent Application Laid-open No. 7-326711 (FIGS. 1 and 5) that does not use a base plate has low stiffness and may encounter a situation in which, when the semiconductor device is fixed to a heat sink by application of a heat dissipating material and subsequent thread fastening or the like, a force is exerted on an insulating substrate, and the insulating substrate becomes warped upward in a convex form (which may be hereinafter abbreviated as “upward convex warpage”). If upward convex warpage occurs in the insulating substrate, there are problems, such as increased thermal resistance between the insulating substrate and the heat sink.
In the semiconductor device disclosed in Japanese Patent Application Laid-Open No. 9-69603 (FIG. 5), the electrode and the outer case are in contact at only a portion where the electrode passes through the upper surface of the case. Hence, the insulating substrate cannot be pressed strongly enough to prevent the occurrence of convex warpage in the electrode inside the case. This does not solve the problems due to upward convex warpage of the insulating substrate with Japanese Patent Application Laid-open No. 7-326711.